Metabolizable Energy Nomenclature for Poultry Feedstuffs

The use of the terms “apparent metabolizable energy” (AME) and “true metabolizable energy” (TME) is confusing and misleading. In proposing the “true” energy system, Harris (1966) confused the conceptual definition of metabolizable energy (ME) (Fraps, 1946) with the experimental techniques and resulting formulae for estimating its value. Metabolizable energy is the feed energy available to the bird for anabolic and catabolic processes. Experimental techniques for estimating ME should obviously correct for endogenous energy loss when it is large enough to influence the results. The ME method of Hill et al. (1960) does this by comparing test and reference diets. The TME method of Sibbald (1976) does this by comparison of fed and fasted birds. Both systems estimate the energy missing from a feedstuff after it passes through chickens: thus, there is no conceptual difference. The differences center on the validity of the corrections, e.g. reference diet for ME and fasted bird for the TME. The nomenclature ME should be used for both systems of estimation with subscripts indicating the method when desired. The use of the word “true” in describing any experimental assay is inappropriate and misleading. Although true can indicate “corrected for error”, it also has other meanings (e.g., “the quality of being accurate”, “without deviation”, and “in accordance with fact or reality”). We propose a nomenclature to facilitate recognition of the strengths and weaknesses of the various assays and to express for what sources of error a given assay has been corrected.